Deformation and break-up of aqueous drops in dielectric liquids in high electric fields

Abstract

In the petroleum industries, high electric fields are used in the separation of aqueous drops from an oil phase. However, high electric fields can also deform and break up the drops. Under a high uniform electric field, a drop is usually a prolate spheroid, but it can also be of different forms such as a lamella penetrating into the continuous phase, or a drop with a flat surface on one side and a cone on the other side. The deformed drop shape depends greatly on the electrical conductivity, viscosity, surface tension and density of both liquid phases. Droplets can be produced from a prolate drop head, while the tail has a lamella penetrating into the continuous phase. The onset of drop break-up occurs at an electric field strength of between 300 and 350kV/m, corresponding to an electric Weber number of between 0.06 and 0.13. The current Weber number needs some modifications before it can be fully applied to characterise the onset of drop break-up. However, the form of the applied electric field is important. With pulsed dc fields, drop deformation and detachment rates are influenced by the field strength and the pulsing frequency.